588 SCIENCE PROGRESS 



with the second interpretation that I suggested in 1906 as an 

 alternative to the qualitative conception, and further developed 

 in 1909. 1 As was pointed out in these papers, many of the 

 difficulties raised by the qualitative conception disappear if we 

 accept the " naive view," directly suggested by the cytological 

 facts, that in the insects the presence of one X-element means 

 per se the male condition, while the addition of a second element 

 of the same kind produces the female condition. The puzzle of 

 the bee is now solved, and we at once comprehend how the 

 elimination of one X-element by the parthenogenetic egg (as 

 in Phylloxera) produces the male condition. 



" In ordinary sexual reproduction all the unfertilised eggs 

 should after maturation bear the male tendency, because one 

 X-element is left in the egg after reduction. If capable of 

 parthenogenesis with the reduced or haploid number of chromo- 

 somes, such eggs should produce males (as appears to be 

 actually the case in the bees and ants). If fertilised by a 

 spermatozoon that lacks the X-element, the egg still produces 

 a male for the same reason. If fertilised by a spermatozoon 

 that contains this element, the egg produces a female because 

 of the introduction, not of a dominant 'female tendency,' but of 

 a second X-element." 2 



Accepting this view we may designate the female as the plus 

 sex, the male as the minus. In current Mendelian terms, the 

 female Protenor or Anasa is cytologically " homozygous," arising 

 by the union of like plus gametes (each containing X) and again 

 producing gametes of this type only ; while the male is " hetero- 

 zygous," arising by the union of a plus gamete and a minus, 

 and producing these two classes in equal number. 3 To employ 

 a more recent and perhaps in this case preferable terminology, 

 in respect to the X-element the female is of "duplex" constitu- 

 tion, the male of " simplex." 



This view equally accounts for all the facts in the sexual 

 reproduction of the forms under consideration, and for many 



1 Science, January 8. 



1 Wilson, op. cit. 



3 This use of the terms " homozygous " and " heterozygous " is the reverse of the 

 one employed by Morgan in the discussion appended to his paper on Phylloxera^ 

 already cited. It seems to me to be justified both by the etymology of the word 

 and by Bateson's definition, given at p. 16 of Mendel's Principles. Morgan had 

 in mind the fact that the parthenogenetic female may produce males as well as 

 females ; but this is, I think, equally consistent with the terminology here employed 

 for the cytological conditions. 



